When you consider the difference between a human being and a machine, you start with some idea about what it is to be a human being and what it is to be a machine. Some people now celebrate the technological advances that can make it hard to tell the difference; others view that difficulty with anxiety. They are concerned when machines do what we want to do; and they have species-self-doubt when machines do things that once defined what it was to be uniquely human. The worst worry is that the machines will refuse our orders, that they may acquire a will of their own, and want free agency.

You start out with some matter-of-fact presumptions about what each sort of entity really is. If you’re reading this piece, you’re almost certainly a person, and you assume that its other readers are too. you might be reading it on a machine, just as I wrote it on a machine, and it was typeset on a machine. I didn’t have a problem knowing that my laptop was a machine, but I’d be hard put to define human beings and machines such that the definitions of each were distinct, clear, up to date with the latest technological advances, and would pass muster with the artificial intelligence experts and cognitive psychologists who theorise about these things for a living.

Some time ago, it was confidently said that people uniquely have ‘intelligence,’ or ‘rationality,’ or that they possess ‘language,’ or that they have ‘feelings,’ or even that they can ‘adapt flexibly to changing situations,’ while machines have none of these competences. These days, I can’t be te only one who sometimes feels a bit unsure about these distinctions. I have a cheap chess-playing programme that usually beats me; I know that IBM’s Deep Blue beat Gary Kasparov and that DeepMind’s AlphaGo beat the human Go master. Sometimes I get angry at my car’s satnav device: she seems to me a little too prissy and self-satisfied, and thinks she knows best how to get around my own town. (I don’t think of her as stupid, just as having an agenda of her own.)

These things have a deep history, and Jessica Riskin’s wide-ranging, witty and astonishingly learned book aims to recover it. People in the past thought in radically different ways from the way we do now about what it is to be a human being and a machine, and none of these past sensibilities was uncontested in its own time. In any period from at least the late Middle Ages through to the 19th century, arguments about the properties of humans and machines were invariably drawn into discussions about animals and about divine agency. Each entity of the terrad (humans, machines, animals and God) was considered relationally: to know the properties of any one was to imply something about the properties of the others. In the 17th century, for example, to be human was to be a little lower than the angels but—because of God’s intentions and creative acts—much higher than the beasts. New tendencies in 17th-century philosophy and science pictured nature, animals and human bodies as divinely designed machines, though there was conflict over whether anything in nature could be explained in mechanical terms, whether only some things were machine-like, or whether ‘mechanical nature’ was just a metaphorical way of speaking.